The eldritch invocation Shroud of Shadow from the UA: Revised Class Options reads as follows:
You can cast invisibility at will, without expending a spell slot.
Similar abilities such as a wizard's spell mastery specify that the caster can only cast the at-will spells at their lowest spell level:
You can cast those [at will] spells at their lowest level without expending a spell slot when you have them prepared.
Shroud of Shadow has no such clause. So can this invisibility spell be cast at a higher level?
Best Answer
Spells cast without a spell slot are cast at their lowest level. And no, you can't cast it at a higher level because to do so would require you to expend a higher level spell slot.
From page 12 of the Sage Advice Compendium: